#bkcenter{
    position: fixed;
    width: 1200px;
    height: 100%;
    left: 50%;
    top: 0;
    bottom: 0;
    /* border: solid 1px red; */
    background-image: url('../images/background_img/a1.png');
    background-repeat:no-repeat;
    background-size: 100% 100%;
    margin-left: -600px;
    z-index:0;
}
#bkleft{
    width: 340px;
    position: fixed;
    right:50%;
    left: 0;
    top: 0;
    bottom: 0;
    margin-right: 600px;
    /* border: solid 1px blue; */
    background-image: url('../images/background_img/a11.png');
    background-repeat: no-repeat;
    background-size: 100% 100%;
    z-index: 0;
}
#bkright{
    width:420px;
    position: fixed;
    left:50%;
    right: 0;
    top: 0;
    bottom: 0;
    margin-left: 600px;
    /* border: solid 1px blueviolet; */
    background-image: url('../images/background_img/a9.png');
    background-repeat: no-repeat;
    background-size: 100% 100%;
    z-index: 0;
}